Evaluation of the physicochemical parameters of edible oils sold in the three cities of Burkina Faso

Abstract The edible oil needs of African countries are met by imported or locally produced ones. Therefore, consumers are generally confronted with a choice of edible oils of poorly controlled quality. However, quality control of edible oils for local consumption is of high necessity. This study aimed to assess the quality of edible oils sold and consumed in some cities in Burkina Faso. Oil samples collected in the cities of Dédougou, Koudougou, and Nouna were used for several analyses. Oil samples from palm, refined and unrefined cottonseed, and groundnut were collected. Standard methods were used to assess the physicochemical quality parameters of the oils, including the peroxide value, water and volatile matter content, acid value, traces of soap, and mineral oil contents. The parameters varied significantly depending on the oil type, but not by the locality of origin. The peroxide indices had varied from 3.24 to 39.99 mEq O2/kg oil. The acid indices varied from 0.22 mg KOH/g to 1.24 mg KOH/g. The water and volatile matter contents ranged from 0.04% to 0.88%. The test for traces of soap gave values ranging from 0 to 76 ppm. For the mineral oil test, four samples of cottonseed oil collected in Dedougou gave positive results. Compared to international reference standards, in particular the Codex Alimentarius standard, it may constitute a health risk for consumers. The poor storage, distribution, and marketing conditions of the oils could explain their poor quality. In order to provide consumers with quality oils, regular controls must be undertaken in the places where the oils are stored and/or marketed.


| INTRODUC TI ON
Edible oils play an essential role in our diet. In addition to providing a nutritional function, they contribute to energy supply and are sources of essential fatty acids particularly linoleic and alpha-linolenic acids (Okparanta et al., 2018). They also participate in the supply and transport of fat-soluble vitamins including A (in terms of carotenoids), D, E, K, and other constituents of nutritional interest such as phytosterols or phenolic compounds especially for vegetable oils (Mengistie et al., 2018). This high nutritional potential of oils is due to their stability (Benmohamed et al., 2020).
In Burkina Faso, vegetable edible oils are essentially made up of locally produced oils and imported ones. During 2009-2010, the demand for oil on the Burkinabe market was in the order of 60,000-65,000 tons,

| Brief presentation of the collection zones and biological materials
The city of Koudougou has approximately 183,332 inhabitants, Dedougou has 118,727 inhabitants, and Nouna has 95,599 inhabitants. Samples (60) were collected in the above three cities (20 samples/city). The distribution of the samples in Koudougou is as follows: 2 of groundnut oil, of 2 unrefined palm oil, and 16 of refined palm oil; the in Dédougou: 12 of refined palm oil and 08 of refined cottonseed oil; in Nouna: 7 of refined cottonseed oil, 9 of refined palm oil, 2 of groundnut oil, and 2 of unrefined palm oil.

| Peroxide value measurement
Peroxide value is a measure of peroxides contained in the oil. It is determined by measuring iodine released from KI. A known measured weight of oil samples is dissolved in acetic acid then chloroform and saturated KI mixture are added to the sample and the amount of iodine liberated from KI by the oxidative action of peroxides present in the oil is determined by titration with standard sodium thiosulphate using starch solution as an indicator (AOAC, 1984).

| Determination of the moisture and the volatile matters content
The moisture and the volatile matters content is according to standard (ISO, 2016).

| Determination of the acid value
The fat matters alter themselves by aging while giving birth by hydrolysis to free fatty acids. The acidic value of an oil is determined by titration of the free fatty acids with the help of an ethanolic solution of potassium hydroxide (ISO 660, 2020).

| Determination of the soap traces
It is defined as the content of the soap in the oil that is soluble in the acetone with 3 to 4% of water expressed in part by million (ppm): it informs on the efficiency of the separators.

| Discussion
The moisture and volatile matter contents of samples ranged from 0.04% to 0.88% ±0.22. Among samples, 35% from Koudougou, 25% from Dédougou, and 15% from Nouna displayed values higher than the maximum value for moisture and volatile matter content set by the Codex Alimentarius and those reported elsewhere (Hasan et al., 2018); but they are similar to data found by Odoh et al. (2017).
These high levels could be related to the extraction processes and could influence the conservation of the oil by promoting the hydrolysis of free fatty acids and their oxidation (Odoh et al., 2017).
Indeed, oil undergoes more significant alteration during storage such as acidification, oxidation, and is conducive to the development of microorganisms (Macarthur et al., 2021) (Figure 13).
The peroxide value of the refined oils varies from 3.24 to 39 mEqO 2 /kg with averages of 8.52 O 2 /kg mEq, 9.31 O 2 /kg mEq, and 10.92 O 2 /kg mEq for the Koudougou, Dédougou, and Nouna samples. These data are similar to those found by Almeida et al. (2019).
However, 30% of samples showed values above 10 mEqO 2 /Kg, the maximum value set by the Codex Alimentarius for refined oils, which would indicate advanced oxidation for these samples. It is known that oxidative deterioration of oils occurs much faster when stored at high temperature and exposed to light than under other storage conditions (Almeida et al., 2019). Nevertheless, these findings are different from those found elsewhere (Chiboret al., 2018;Tańska et al., 2016). According to these analyses, high temperature, visible light, and oxygen can easily increase the peroxide value of oils. Oils with a peroxide value greater than 15 meqO 2 /kg may be dangerous to health by increasing reactive oxygen species as well as secondary products of lipid peroxidation, which are sources of cardiovascular and inflammatory diseases (Konuskan et al., 2018).
For the acid indices of refined oil samples, they ranged from 0.22 to 1.24 mg KOH/g with respective averages of 0.58 mgKOH/g, 0.53 mgKOH/g, and 0.5 mgKOH/g for Koudougou, Dédougou, and Nouna, respectively. For unrefined oil samples, the value ranged from 0.08 mgKOH/g to 0.84 mgKOH/g. This may be due to the presence of endogenous enzymes and antioxidants that prevent the hydrolysis of fatty acids (Benguendouz et al., 2017). Of all refined oil samples, 20% had acidity values greater than 0.6 mg KOH/g, the maximum value set by the Codex Alimentarius; while for unrefined oils these acidity values are lower than the maximum value, 4 mg- According to Kharroubi Mariem and Bellali Fatima (2017), chemical neutralization has been widely applied in the industry to remove free fatty acids in vegetable oils. This results in a loss that is increased by the binding of the oil to the soap formed (Mariem & Fatima, 2017). The high soap content in samples DC4, DC5, and DC6 is due to the non-control of the refining process or the use of inadequate materials. These oils should be removed from the consumer market, as they may pose a health risk to the consumer. The presence of trace amounts of soap in peanut oils may be due to contamination with the use of recycled soap-washed containers.
As for the search for mineral oils, we found that four cotton sam-